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    <p>When you use the <code>java</code> command to run a Java application from the command line, e.g.,</p> <pre><code> java some.AppName arg1 arg2 ... </code></pre> <p>the command loads the class that you nominated, and then looks for the entry point method called <code>main</code>. More specifically, it is looking for a method that is declared as follows:</p> <pre><code>package some; public class AppName { ... public static void main(String[] args) { // body of main method follows ... } } </code></pre> <p>The specific requirements for the entry point method are:</p> <ol> <li>The method must be in the nominated class.</li> <li>The name of the method must be "main" with <em>exactly</em> that capitalization<sup>1</sup>.</li> <li>The method must be <code>public</code>.</li> <li>The method must be <code>static</code> <sup>2</sup>.</li> <li>The method's return type must be <code>void</code>.</li> <li>The method must have exactly one argument and argument's type must be <code>String[]</code> <sup>3</sup>. </li> </ol> <p>The argument <em>may</em> be declared using varargs syntax; e.g. <code>String... args</code>. See <a href="https://stackoverflow.com/a/36803396/139985">https://stackoverflow.com/a/36803396/139985</a>. The <code>String[]</code> argument is used to pass the arguments from the command line, and is required even if your application takes no command line arguments.</p> <p>If any one of the above requirements is not satisfied, the <code>java</code> command will fail with the message:</p> <pre><code>java.lang.NoSuchMethodError: main Exception in thread “main” </code></pre> <p>If you encounter this error, check that you have a <code>main</code> method and that it satisfies all 6 of the requirements listed above.</p> <hr> <p><sup>1 - One really obscure variation of this is when one or more of the characters in "main" is NOT a LATIN-1 character ... but a Unicode character that <em>looks like</em> the corresponding LATIN-1 character when displayed.</sup></p> <p><sup>2 - See <a href="https://stackoverflow.com/q/146576/781723">Why is the Java main method static?</a> for explanation of why the method is required to be static.</sup></p> <p><sup>3 - <code>String</code> must correspond to <code>java.lang.String</code> and not a custom class named <code>String</code> hiding it.</sup></p>
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    1. USStephen C
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    1. COThe class doesn't have to be public actually. At least not in practice, I don't know maybe there's a spec that requires it but `java` can invoke a non-public class that has a public main method.
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      1. USMark Peters
    2. COThanks ... updated.
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